The present invention relates to a lead out structure for a lead circuit section connected to a flexible printed circuitry housed in a casing of a switch unit.
Door trims for vehicles such as automobiles are normally provided with electrical equipment such as a switch unit including power window switches for use in opening and closing window glasses, door mirror driving switches and so on; and courtesy lamps that are switched off when doors are shut and switched on when opened. In order to connect these kinds of electrical equipment, the door trim is rigged with a number of electric wires and connectors. Such wiring operation is very troublesome because it is carried out blindly through the working window of a door panel. Moreover, many parts for use in electrical mechanism-to mechanism connection are required, which will also result in arduous work of incorporating and connecting them.
In consequence, there has recently been employed a flat circuitry for wiring to complete the connection of electrical equipment (e.g., Japanese Patent Publication No. 9-309390A). A switch holder 1 in a related flat circuitry has been so configured as shown in FIG. 4.
In FIG. 4, the upper-side terminal section 3 of a flexible printed circuitry 2 is bent at a right angle and inserted into and fixed to a switch holder 1. The flexible printed circuitry 2 includes a plastic insulating film 4 and a plurality of parallel printed circuits 5 arranged in the insulating film 4. Further, an engagement hole 6 is bored in four corners of the insulating film 4 and a plurality of contacts 7 following the respective printed circuits 5 are provided in the upper-side terminal section 3 of the flexible printed circuitry 2.
The plastic switch holder 1 comprises a rectangular base plate 8 and a frame-like cover 9 that is pivotal with respect to the base plate 8. The cover 9 is coupled to the base plate 8 by, for example, thin-walled hinges that are integral therewith. A frame wall 10 is uprightly provided to both sides of the base plate 8. Further, an elastic retaining arm 12 and a curved elastic flap 13 with respect to a door trim 11 are projected from the outer wall face of each frame wall 10. In other words, the elastic retaining arm 12 is provided on the rear end portion of each frame wall 10, whereas the elastic flap 13 is provided on the front end portion thereof. Each elastic retaining arm 12 has a retaining projection 14 and a releasing member 15. Moreover, engagement holes 17 with respect to the locking projections 16 provided to the cover 9 are formed in the frame wall 10.
Positioning pins 19 each having conical tilted guide faces 18 relative to the respective retaining holes 6 of the flexible printed circuitry 2 are projected from the base plate 8. Further, an opening 20 is provided in the cover 9, so that the contacts 7 of the flexible printed circuitry 2 and the positioning pins 19 can be located within the opening 20. Incidentally, the tilted guide face 18 may be continuous from the upper to lower ends of the positioning pin 19.
The terminal section 3 of the flexible printed circuitry 2 is positionally mounted on the base plate 8 by mating the engagement holes 6 with the respective positioning pins 19. Then the locking projections 16 are fitted in the respective engagement holes 17 by closing the cover 9, which is locked in such a condition that it clamps the terminal section 3. The positioning pins 19 are so positioned as to project within the opening 20. Due to the positioning pins 19, the contacts 7 are precisely positioned.
FIG. 5 shows a state wherein a flat circuitry 21 has been incorporated in the door trim 11. More specifically, an opening 22 is formed in the door trim 11, and a pair of insertion guides 23 with respect to the switch holder 1 of the flat circuitry 21. are provided in the direction of thickness of the door trim 11. The insertion guides 23 are L-shaped and projected from the upper wall 24 within the opening 22. Moreover, an engagement hole (not shown) is formed in each insertion guide 23 with respect to the retaining projection 14 of the elastic retaining arm 12 of the switch holder 1. The switch holder 1 is supported by the elastic retaining arms 12 and the elastic flaps 13 between the pair of insertion guides 22 so as to be movable in the widthwise direction thereof.
The flexible printed circuitry 2 is made immovable by fitting the positioning pins 19 in the engagement holes 6 respectively provided in the four corners of the insulating film 4 and holding down the flexible printed circuitry. 2 with the cover 9.
The flexible printed circuitry 2 is prepared by printing switching circuits on the film to form an extremely thin contact switch. Although the flexible printed circuitry 2 is immovably fixed by fitting the positioning pins 19 in the respective engagement holes 6 and made immovable by holding it down with the cover 9, the film-like lead circuit section is drawn from the switching circuit section. Consequently, the film-like lead circuit section is strong enough to withstand the tensile force applied in its longitudinal direction. When force is applied in a direction perpendicular to the longitudinal direction of the film-like lead circuit section (in its widthwise direction), however, excessive force as tensile stress is to be applied to one side portion of the circuit section.
When the tensile stress is applied from the outside to the flexible printed circuitry 2 like this, the operating switches may not easily be turned on as the switch contacts become displaced. When further excessive tensile stress is applied from the outside to the flexible printed circuitry 2, the problem is that the disconnection of switching circuits occurs.
It is therefore an object of the present invention is provide a structure wherein a switching circuitry is formed integrally with a lead circuitry whereby to prevent stress from being applied to the switching circuitry even when tensile stress is applied to the lead circuitry while the lead circuitry is being wired and conveyed, to prevent the switching circuitry from being displaced even when excessive stress acts on the lead circuitry; and to prevent the lead circuitry from being broken even when excessive stress acts on the lead circuitry.
In order to accomplish the object above, according to the present invention, there is provided a structure comprising:
a flexible printed circuitry including a lead circuit section integrally provided with a switch circuit section, and at least one engagement hole is formed on a part of the lead circuit section;
a lower casing having a side wall provided with a cut out portion from which the lead circuit section is led out, and at least one boss formed in the form of S-shape, to which the engagement hole is fitted to mount the flexible printed circuitry thereon; and
an upper casing combined with the lower casing to constitute a casing which serves as a switch circuit unit, the upper casing having at least one hold-down member engaged with the boss to hold down the lead circuit section onto the lower casing.
Since the switching circuitry is formed integrally with the lead circuitry whereby it is possible to prevent stress from being applied to the switching circuitry even when tensile stress is applied to the lead circuitry while the lead circuitry is being wired and conveyed; to prevent the switching circuitry from being displaced even when excessive stress acts on the lead circuitry; and to prevent the lead circuitry from being broken even when further excessive stress acts on the lead circuitry.
Preferably, at least three engagement holes are formed on the lead circuit section so as to be arranged in a longitudinal direction thereof with predetermined intervals. The lead circuit section is folded such that all the engagement holes are fitted with the boss to be mounted on the lower casing while providing surplus length portions in the vicinity of the boss, and then led out from the cut out portion.
Preferably, a pair of the at least three engagement holes are formed on the lead circuit section at both end portions in a widthwise direction thereof. A pair of bosses are formed on the lower casing so as to fit with the respective at least three engagement holes. A pair of hold-down members are formed on the upper casing so as to engage with the respective bosses.
Accordingly, even when tensile stress is applied to the lead circuit section while the lead circuit section is being wired or conveyed, such stress can be absorbed by the engagement holes and further stress can be absorbed by the surplus length portion. Therefore, the stress is prevented from being applied to the switching circuit section and even when the excessive stress acts on the lead circuit section, the displacement and breakage of the switching circuit section can be prevented.
Preferably, the hold-down member is a tubular member into which the boss is fitted.
Since the front end of the hold-down member holds down the lead circuit section fitted with the engagement hole, tensile stress applied to the lead circuit section while the lead circuit section is being wired or conveyed can be further surely absorbed. Therefore, the stress is prevented from being applied to the switching circuit section and even when the excessive stress acts on the lead circuit section, the displacement and breakage of the switching circuit section can be prevented.
Preferably, reinforcing dummy patterns are formed on the flexible printed circuitry at both end portions in a widthwise direction thereof.
Since the lead circuit section is formed with reinforcing dummy patterns capable of withstanding tensile stress, the breakage of the lead circuit section, and the displacement of the switching circuit section can be surely prevented.
Preferably, a protective film or a copper foil is formed on the lead circuit section so as to surround the engagement hole.
Since force is applied most strongly to the engagement hole formed in the lead circuit section when the lead circuit section is being wired or conveyed, the provision of the protective films or copper foils on the peripheries of the engagement hole can prevent the breakage of the engagement hole and the displacement of the switching circuit section.
According to the present invention, there is also provided a method comprising the steps of:
preparing a flexible printed circuitry including a lead circuit section integrally provided with a switch circuit section, and at three engagement holes are arranged on a lead circuit section in a longitudinal direction thereof with predetermined intervals;
preparing a lower casing having a side wall provided with a cut out portion from which the lead circuit section is led out, and a boss formed in the vicinity of the cut out portion;
folding the lead circuit section such that all the engagement holes are fitted with the boss while providing surplus length portions in the form of S-shape in order to mount the flexible printed circuitry onto the lower casing;
leading out the lead circuit section from the cut out portion; and
combining an upper casing having a hold-down member with the lower casing such that the hold-down member engages with the boss to hold down the lead circuit section onto the lower casing.